Composition and physico-chemical characteristics of goat milks containing the A or O αs1 casein variants

Abstract

The composition of goat milks originating from three animals homozygous for αs1 casein, variant A, and from three others, homozygous O, was compared monthly over a lactation. Mean fat value was higher by 4.7 g kg-1 in A milk, the difference between A and O reaching 9.8 g kg-1 in the early lactation. Total nitrogen matter was higher by 6.8 g kg-1 in A milk on the whole lactation. Total casein levels in A and O milks were respectively 21.2 and 17.8 g kg-1. Caseins (CN) other than αs1 were at similar levels in the two groups of milks, αs1CN was -5.2 g kg-1 in A milk and ∼ 0.0 g kg-1 in O milk. Mineral contents showed a high individual variability. Rennet coagulation tests led to higher firming rates and higher firmness in A milks, while coagulation time was not different between A and O milks. Total fatty acid proportions in milks were different: more short and medium length saturated fatty acids in A milk, balanced by a lower C16 level. Lipolysis was by far lower in A milk and the relative proportion of fatty acids in the free fatty acid fraction was different in A and O milks, meaning a difference in lipase level and/or in lipase specificity due to the enzyme itself or to its environment. In contrast, proteolysis of the plasmin type was higher in A milks. © Inra/Elsevier, Paris.